A linear sensor measures an external perturbation by producing a system output that varies linearly with the external perturbation. A fixed scale factor can be used to describe the linear relationship between the external perturbation and the external output. The system output of the linear sensor can also include a fixed offset. However, both the scale factor and offset of the linear sensor can change over time due to many factors. These factors include changes in mechanical compliance due to temperature, long-term mechanical creep, changes in packaging pressure of sensors due to imperfect seals or internal outgassing, changes in quality factors of resonators, drift of one or more amplifier gain stages, capacitive charging effects, drift on bias voltages applied to the sensor, drift on any internal voltage reference required in a signal path, drift of input offset voltages, drift of any required demodulation phase and gain, and the like. In linear sensors, changes in the scale factor or the offset will result in changes in the system output, even if the external perturbation is not changed. This causes accuracy of linear sensors to degrade over time.
Controlling drift of sensor system output is important in many applications, especially those requiring performance at low frequencies. Low frequency, or 1/f, noise reduces low frequency performance. High levels of 1/f noise limit a sensor's ability to measure low frequency signals that may be masked by the 1/f noise. For example, navigation systems require good low-frequency performance with low 1/f noise and low drift. Because many useful navigation signals appear in the low frequency end of the spectrum, these must be accurately measured to compute position.